Week4 - 1 1 CSE 3402 Winter 2012 Fahiem Bacchus...

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Unformatted text preview: 1 1 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance CSE 3402: Intro to Artificial Intelligence Game Tree Search Required readings: Chapter 5, sections 5.1, 5.2, 5.3, 5.7. 2 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Generalizing Search Problems So far: our search problems have assumed agent has complete control of environment state does not change unless the agent (robot) changes it. makes a straight path to goal state feasible. Assumption not always reasonable stochastic environment (e.g., the weather, traffic accidents). other agents whose interests conflict with yours 2 3 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Generalizing Search Problems In these cases, we need to generalize our view of search to handle state changes that are not in the control of the agent. One generalization yields game tree search agent and some other agents. The other agents are acting to maximize their profits this might not have a positive effect on your profits. 4 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Two-person Zero-Sum Games Two-person, zero-sum games chess, checkers, tic-tac-toe, backgammon, go, l find the last parking space z Your winning means that your opponent looses, and vice-versa. Zero-sum means the sum of your and your opponent ` s payoff is zero---any thing you gain come at your opponent ` s cost (and vice-versa). Key insight: how you act depends on how the other agent acts (or how you think they will act) and vice versa (if your opponent is a rational player) 3 5 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance More General Games What makes something a game? there are two (or more) agents influencing state change each agent has their own interests e.g., goal states are different; or we assign different values to different paths/states Each agent tries to alter the state so as to best benefit itself. 6 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance More General Games What makes games hard? how you should play depends on how you think the other person will play; but how they play depends on how they think you will play; so how you should play depends on how you think they think you will play; but how they play should depend on how they think you think they think you will play; 4 7 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance More General Games Zero-sum games are l fully competitive z if one player wins, the other player loses e.g., the amount of money I win (lose) at poker is the amount of money you lose (win) More general games can be l cooperative z some outcomes are preferred by both of us, or at least our values aren ` t diametrically opposed We ` ll look in detail at zero-sum games but first, some examples of simple zero-sum and cooperative games 8 CSE 3402 Winter 2012 Fahiem Bacchus & Yves Lesperance Game 1: Rock, Paper Scissors Scissors cut paper, paper covers rock, rock...
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Week4 - 1 1 CSE 3402 Winter 2012 Fahiem Bacchus...

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